People all across the country are being told on a daily basis that their thyroid gland just died or stopped working. Some patients just accept this without question. Others ask how this could happen. The usual response by their doctor is that it is just something that happens. Almost as if the thyroid gland was a light switch that could just be turned off. Thyroid glands do not just stop working and die for no apparent reason.
Well, because the f/stop is a ratio of the focal length to diameter, our 50mm lens at f/2.8 would have a diameter of 50/2.8 = 17.86mm. Remember, we have to divide that by 2 to get the radius of 8.93mm, so the area of the circle thus formed would be Ï X 8.932, or 250.5 square mm.
Manual focus (MF). Manual focus (MF) is the function that lets the photographer adjust the focus manually, instead of the camera adjusting it. Although autofocus (AF) shooting is more typical in digital cameras, MF is effective when focusing is difficult with autofocus, such as in macro shooting.